Cut It Tall and Let It Fall

There’s good science to my advice

By Dr. Francis Gouin

My annual recommendation for lawns is cut it tall and let it fall. To understand why cutting height makes a difference, consider that each blade of grass is a factory.
A tall blade of grass contains more chlorophyll and is capable of manufacturing more sugars and other metabolites than a short blade of grass. When you set your lawnmower to cut your grass no less than four inches, each blade remains a bigger factory, capable of manufacturing more of what it needs for good growth.
So cut it tall and let it fall.
Combine this practice with cutting your lawn when it reaches a height of six inches, so that you remove only one-third the length of each blade. Now you’ve minimized the size and quantity of grass clippings. These short grass clippings will filter down through the newly mowed lawn faster than longer grass clippings. When it comes to recycling nutrients contained in the grass clippings, four-inch-tall blades shade the soil better than grass blades only one inch tall. Better-shaded soil remains cooler, which minimizes the loss of water by evaporation. The added benefit of cooler soils and reduced water loss by evaporation means that the grass clippings that fall to the ground have a better chance of composting.
As the clippings decompose, nutrients are released and return to the soil where the roots can absorb them. There is some loss of nitrogen, as well as all other nutrients, but at least two-thirds of the nutrients in the grass clippings are recycled.
Another benefit to cutting your lawn tall is that the taller the grass, the deeper the roots. Deeper roots have greater access to moisture farther down in the soil. This makes your lawn more drought-resistant.
Cutting it tall and letting it fall significantly reduces the need for you to apply fertilizers to keep your lawn green and healthy. This practice also significantly reduces your need to irrigate.
Reducing fertilizing and watering gives lawn diseases such as fusarium less chance to become established. On-site composting also helps maintain the desirable microorganisms that work to prevent diseases such as fusarium.

Ask Dr. Gouin your questions at DR.FRGouin@gmail.com. All questions will appear in Bay Weekly. Please include your name and address.